[MlMt] TIP: Resetting per-mailbox column state

[Bill Cole]

I expect Benny will give me a proper slapping if this is substantially 
wrong, but I think this is worth sharing since I wasted a few hours 
trying to find a better fix for what is probably the result of a 
scale-sensitive bug.

PROBLEM: Many of my most frequently used IMAP folders refused to retain 
column settings. Whenever I switched out of them, the next time I used 
them they'd show a collection of columns which may have made sense to me 
at some time when I was debugging a smart mailbox but made no sense for 
normal use. For some time I have been in the habit of using "Revert to 
Default Columns" reflexively and even leaving multiple viewers open just 
to avoid that.

SOLUTION: Nothing subtle. I spent a few hours trying to work out what 
precisely was wrong and find a fix, but nothing worked. My final act of 
desperation, accepting that I would at a minimum lose all per-mailbox 
column settings, was this:

     defaults delete com.freron.MailMate MmMailboxRelatedStates

And that did the trick. Yes, all my per-mailbox column settings were 
gone, but whatever was causing trouble in that dictionary of settings 
structures for 261 mailboxes also went away. Problem solved. As I read 
the labels inside those structures, there seems to be nothing other than 
display tweaks lost in whacking the whole thing, and doing so restored 
my ability to make settings stick.